1. Field of the Invention
The invention is for a system and method for providing a resistive shunt that provides for connecting two terminals within a light socket of a light string when the bulb is removed. Essentially, a resistive element is included as part of or comprises the socket bridge itself such that when the light bulb is removed, the electrically resistive element is provided in series with the bridge so as to present the same resistance between the external socket leads as that provided by the bulb when it is inserted into the socket and operational. In this manner, the overall resistance characteristics of the light string are not changed upon the removal of one or more bulbs in the light string and power/current demand increases are avoided within the light string system upon bulb removal.
2. Description of the Prior Art
Holiday light strings are an omnipresent facet of many holiday decoration displays. Safety is one of the primary concerns in designing these light string systems. In particular, the removal of bulbs from the sockets within which the bulb typically resides presents several practical operational problems as well as safety concerns. Numerous bridging technologies exist that provide for a closed circuit condition within the socket when bulbs are removed such that the remaining bulbs in the light string remain lit. For Example, U.S. Pat. No. 7,591,658 issued on Sep. 22, 2009 to Chen (hereinafter “Chen”) provides one such shunting system in which one of the legs of an electrically conductive torsion spring is moved into a bridging position connecting the internal socket leads when the bulb is removed from the socket. One problem with this arrangement, however, is that the torsion spring is typically made of copper or another low resistance conductor. Thus, the removal of the bulb, including its associated filament resistance, causes the current drawn by the light string to increase upon bulb removal. If numerous bulbs are removed from a string, this problem increases, potentially to the point of dangerous operation. Commercial light string systems are typically rated for a maximum current draw or power consumption, and any increases up to or over those limits may be considered a safety hazard.
Underwriters Laboratories (UL) is a safety consulting and certification company that provides safety-related certification, validation, testing and inspection services. The organization advises and trains manufacturers of commercial manufacturers on various safety-related topics. UL certification is often a requirement for commercially distributed electrical systems to be offered to the public. Many retail outlets that offer holiday light string systems, for example, require that the light strings and components offered by their manufacturers pass UL certification as a condition of being offered for sale in their retail establishments. Numerous other worldwide certification organizations exist that provide similar functions and services.
Maximum light string current draw or power consumption is one of the most recent safety requirements to be formulated by electrical safety, standards-setting bodies. UL 588, for example, covers seasonal and holiday decorative products, specifically “factory-assembled seasonal lighting strings with push-in, midget-screw, or miniature-screw lamp holders connected in series for across-the-line use or with candelabra- or intermediate-screw lamp holders connected in parallel for direct-connection use . . . . [and] which are portable and not permanently connected to a power source.” To achieve UL certification under this specification section, a shorting test of light sockets shunts is conducted wherein bulbs are removed one at a time until many bulbs are removed from a single string. To achieve UL certification under this standard, the current of the light string shall not increase beyond a certain percentage, typically 10%.
Thus the need exists in the industry in which a shunting mechanism is provided, within a bulb socket and external to the bulb itself, such that the resistive characteristics of the shunt mirror those of the removed bulb. This may be as simple as matching a resistance of the two. In more complicated systems, the bulb circuitry can be mirrored within the shunting mechanism itself. In any case, any number of bulbs may be removed from the light string containing such a system without appreciable increased in current or power dissipation, thereby achieving the goals of the above-mentioned standards organizations and creating a safer light string system.